Conventionally, there is technology for motion detection for detecting the motion of an object. In conventional motion detection, moving objects are captured by taking differences between images captured at predetermined frame intervals. Thus, the motion of the object can be detected only at intervals of flames in conventional motion detection. In other words, it is not possible to sequentially detect the motion of the object.
Therefore, in recent years, for example, as disclosed in “A 240×180 10 mW 12 us latency sparse-output vision sensor for mobile applications,” VLSI Circuits (VLSIC), 2013 Symposium on, Publication Year: 2013, Page(s): C186-C187 (hereinafter referred to as “Document 1”), technology of a solid-state imaging device configured to achieve both motion detection for sequentially detecting motion of an object and normal photographing, by detecting a change in a signal according to the motion of the object has been proposed. In the solid-state imaging device proposed in Document 1, each pixel includes one photoelectric conversion element (photodiode) configured to photoelectrically convert incident light and it is possible to asynchronously perform active pixel sensor (APS) reading for reading a charge signal in the normal photographing and address event representation (AER) reading for reading a charge signal for motion detection.
In the solid-state imaging device proposed in Document 1, a change over time in the charge signal photoelectrically converted by the photodiode is detected at the time of motion detection, and a pulse signal indicating the direction in which the charge signal changes is output only from a pixel in which the magnitude of the charge signal exceeds a predetermined threshold value through AER reading. In other words, in the solid-state imaging device proposed in Document 1, a pulse signal indicating an increase/decrease of the magnitude of the charge signal is output through the AER reading. At this time, address information indicating the position of the pixel configured to output the pulse signal is also added to the pulse signal output through the AER reading. In other words, address information indicating a pixel position at which motion of the object is detected is also added to the pulse signal output through the AER reading.
Thereby, in the solid-state imaging device proposed in Document 1, the pixel position at which the motion of the object is detected can be extracted at an asynchronous timing irrespective of a timing of a frame from which the charge signal is read in the normal photographing. Thereby, in the solid-state imaging device proposed in Document 1, it is possible to acquire a moving object at a rate higher than a frame rate in the normal photographing.